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The U.S. space agency NASA has postponed the launch of its newest rocket, the Ares I-X, because of weather concerns.

Space agency officials at the Kennedy Space Center in the southeastern U.S. state of Florida rescheduled the launch several times Tuesday, but cloud cover moved in and forced the agency to postpone the mission as the launch window closed.

Launch Director Ed Mango said they will try again on Wednesday, when weather is expected to be better.

Technical and other issues also created problems for Tuesday's launch.  At one point, a cargo ship sailed into the "danger area" off the coast of Florida, but the vessel was contacted and left the zone, and the countdown resumed.

Once it is finally launched, NASA engineers hope to learn valuable information about the Ares I-X's performance from the 700 sensors installed in the rocket.

The flight of the Ares I-X rocket will last only two minutes before it falls into the Atlantic Ocean. 

The next-generation rocket is a modified version of the space shuttle's solid-fuel booster rocket and is part of NASA's plan to return astronauts to the moon by 2020, and also to transport crews to the International Space Station.

The rocket may also use its 25 ton payload capacity to deliver resources and supplies to the space station, or to "park" payloads in orbit for retrieval by other spacecraft bound for the moon or other destinations.

The rocket test comes as observers are casting doubt on the future of the U.S. manned space program.

A White House task force says NASA's current $18 billion annual budget has placed the space agency's plans for human space flight on "an unsustainable trajectory."

NASA hopes the first manned mission of Ares will happen by 2015, but the panel says that will not be possible until 2017.

The space shuttle fleet is scheduled to be phased out by 2010.